Such a combined rack and finger are generally intended to allow adjustment of the two elements with respect to each other, knowing that, in normal use, the stresses to which said elements are subjected, tend to maintain the finger engaged in the selected notch of the rack.
When the relative position of these elements is to be changed, the finger must be released from the notch of the rack used up to that moment, said elements must be displaced and the finger must be re-engaged in another notch which corresponds to the new position.
It is important to note that, during the change of position, the elements are free to move. In addition, such change is fairly often decided upon whilst the system is under load, with the result that the operation should be carried out after the system has been unloaded, taking care where one's hands are placed. In fact, if unloading is too rapid, reloading may be effected after release of the finger and/or its re-engagement, and this may then result in a deterioration of the rack; in addition, through lack of attention, a hand may be located between the mobile elements during the manoeuvre and if said released elements move together energetically during reloading, the hand may be pinched and injured.
It is an object of the present invention to overcome these drawbacks by proposing a locking device which maintains the finger in the selected notch of the rack, whether the system is under load or completely relieved, and which can be neutralized only when said system is unloaded and thanks to a manoeuvrable positive control, at a sufficient distance from the mobile elements to avoid one's hand being pinched.